Synergy Effect of Symmetry-Breaking and End-Group Engineering Enables 16.06% Efficiency for All-Small-Molecule Organic Solar Cells
Qian Wang, Xu Zhang, Yawei Miao, Xinyue Jiang, Xunchang Wang, Zhan Zhang, Zekun Lv, Tao Liu, Bingsuo Zou, Huajun Xu, Renqiang Yang, Yuanyuan Kan, Yanna Sun, Ke Gao
Abstract
Molecular innovation is an urgent necessity to realize efficient all-small-molecule organic solar cells (ASM-OSCs). Asymmetric strategy and end-group engineering have been widely utilized for efficient photovoltaic materials with great success. However, the synergistic effect of the asymmetric strategy combined with end-group engineering on blend film morphology and photovoltaic performance remains insufficiently explored. In this vein, two asymmetric small molecule donors with thiophene/thiazolyl side chains and different end-groups of 3-(2-ethylhexyl)-2-thioxo-4-thiazolidinone (Reh) and cyanoacetic acid esters (CA), W2-CA and W2-Reh, were designed to gain insight into the combined effects of symmetry-breaking and end-group engineering. Compared to W2-Reh, W2-CA exhibits a preferable face-on orientation and good bicontinuous phase-separated morphology, which benefit improving carrier mobility and ensuring a high-efficiency charge transfer pathway in the blended films. 16.06% power conversion efficiency (PCE) is achieved in W2-CA-based ASM-OSCs, one of the highest efficiencies reported up to now for binary ASM-OSCs. A promising avenue for high-efficiency small molecule donor design is provided to achieve efficiency ASM-OSCs.